Recording and/or reproducing apparatus with means for establishing an after-recording area

ABSTRACT

Rotary head recording and/or reproducing apparatus in which respective oblique tracks on a record medium are scanned, each track having an information signal area in which information data is recorded and a track following area in which a tracking control pilot signal is recorded. The track following area precedes the information signal area; and in the preferred embodiment, an additional track following area follows the information signal area. The pilot signal is recorded in only a portion of the track following area, the remainder of which has timing sync data recorded therein. In an after-recording mode the timing sync data is reproduced, detected and used as a reference to define an after-record area.

This application is a continuation of application Ser. No. 08/297,229,filed Aug. 26, 1994, now U.S. Pat. No. 5,596,457 which is a division ofapplication Ser. No. 08/026,735, filed Mar. 5, 1993 now U.S. Pat. No.5,426,538.

BACKGROUND OF THE INVENTION

This invention relates to rotary head recording and/or reproducingapparatus of the type which records/reproduces tracks containing aninformation signal area and a track following area, the latter beingused in a reproducing operation to control the tracking of a head as itscans a track and, more particularly, to such apparatus wherein timingsync data is recorded in the track following area for the purpose ofestablishing a precise afterrecord area for the after-recording ofadditional information in the track.

Rotary head recorders have long been used to record video signals and,more recently, to record digital audio signals, the latter beingrecorded on digital audio tape (DAT). In such rotary head recorders,information, such as video information, audio information or multiplexedvideo and audio information are recorded in an oblique track across arecord tape or other record medium and such information may be recordedin analog or digital form. Digital recorders of the rotary head typegenerally provide superior performance characteristics because of theinherent advantages derived from digital recording techniques, namelythe accuracy with which a recorded digital signal may be reproduced andthe ability to rely upon digital error correction techniques, such aserror correction codes, to compensate for errors that, nevertheless, maybe introduced during the recording or reproducing operation. A typicaldigital video recorder, as an example, records at least three types ofinformation in a track: a digital video signal, a digital audio signaland a digital subcode signal which may be used as a control signal, suchas a display control signal. In such digital video recorders, the video,audio and subcode information typically are recorded in time divisionmultiplexed form such that the video information is recorded in a videosection, the audio information is recorded in one or more audio sectionsand the subcode information is recorded in a subcode section in a track.In addition, and to assure reliability during a reproducing operation,it is common to record a pilot signal in one or more additional areas inthe track, such areas being designated automatic track following (ATF)areas.

In one proposal for a digital rotary head recorder, ATF areas aredisposed in advance of the information area (i.e. an ATF area is scannedbefore audio, video and subcode information is scanned) and also inareas which follow the information area. As a rotary head rotates intoscanning relationship with a track, the head begins its scan at a headentering end of the track and the head rotates out of its recordingrelation with the track at a head leaving end. ATF areas are recorded inthe vicinity of the head entering end and the head leaving end,respectively. The pilot signals which are reproduced from the headentering end ATF area and from the head leaving end ATF area are used ina servo loop to adjust the speed at which the tape is transported,thereby assuring that the heads are generally centered over therespective tracks which they scan.

It often is desirable to operate rotary head recorders of theaforementioned type in an after-recording mode. An after-recording modealso is known as a dubbing mode wherein audio information, for example,is after-recorded in a track at a time subsequent to the recording ofvideo information in that track. Such audio information may be atranslation of audio signals from one language to another, thereby"dubbing" such audio information in synchronism with the movement of,for example, a subject's lips. As another example, the audio informationmay be in the form of a "voice over" but, nevertheless, is related tothe video information. Such voice over techniques are well known and arecommonly used in video production, programming and the like. In additionto after-recording audio information, as just described, it also iscommon to record video information or even subcode information in anafter-recording mode. In these after-recording operations it isimportant to define with accuracy the particular area in a track inwhich the audio or video or subcode information is to be after-recorded.For example, if audio information is to be after-recorded, it isimportant that such audio information be recorded only in the allottedaudio sections so as to avoid inadvertent erasure or "over-writing" ofvideo information. Likewise, if video information is to beafter-recorded, it is important that the beginning and end of the videosignal area be defined accurately so that the after-recorded videoinformation is recorded substantially only in the video area and doesnot erase previously recorded audio or subcode information. Likewise, ifsubcode data is to be after-recorded, it is important that the subcodearea be defined accurately so that subcode data is recordedsubstantially only in that area.

Since ATF areas are recorded in preceding and following relation withrespect to information areas (it will be understood that the term"information area" is intended to refer to one or more, or even all, ofthe audio, video and subcode areas), it had been thought that, in anafter-recording mode, the pilot signal normally recorded in the ATF areacan be detected and used to define the appropriate after-recording area.However, the pilot signal typically is nothing more than a burst ofpilot frequency. If that burst is detected at the beginning of the ATFarea and used as a reference from which the after-recording area isestablished, it is expected that the after-recording area will properlybegin at the very beginning of the information area. But, if the pilotburst is not detected until the middle or even the end of the ATF area,then the beginning of the after-recording area may be somewhat delayed.This delay often is quite variable and unpredictable. Consequently, theafter-recording area may begin too late, thus leaving previouslyrecorded information which should have been erased (or overwritten); andthe after-recording area may extend into a section of the track whichshould not have been erased. Thus, by relying upon the accuratedetection of a pilot signal, the precise definition or establishing ofthe after-recording area generally cannot be carried out with a highdegree of accuracy. Hence, desired signals which should not have beenerased by after-recording may, in fact, be over-written. This problem isexacerbated by the fact that the frequency of the pilot signal normallyrecorded in the ATF area is quite low, which means that the pilot signalmight not be accurately detected until a substantial portion of the ATFarea has been scanned.

OBJECTS OF THE INVENTION

Therefore, it is an object of the present invention to provide rotaryhead recording/reproducing apparatus which overcomes the aforenoteddisadvantages, drawbacks and difficulties and permits an after-recordingarea to be established (or defined) accurately and consistently.

Another object of this invention is to provide rotary headrecording/reproducing apparatus which records/reproduces oblique trackscontaining ATF and information areas and which records a pilot signal ina portion of the ATF areas and also records timing sync data in theremainder of the ATF areas.

A further object of this invention is to provide apparatus of theaforementioned type in which the timing sync data includes informationrepresentative of the location thereof in the ATF area, therebyproviding an accurate reference from which the beginning and end ofafter-recording areas may be established.

Various other objects, advantages and features of the present inventionwill become readily apparent from the ensuing detailed description, andthe novel features will be particularly pointed out in the appendedclaims.

SUMMARY OF THE INVENTION

In accordance with this invention, rotary head recording and/orreproducing apparatus is provided with rotary head means to scanrespective oblique tracks on a record medium, such as (but not limitedto) a magnetic tape. Each track includes an information signal areacontaining information data and is preceded by a track following areacontaining a tracking control pilot signal. In a recording mode, thepilot signal is recorded in a portion of the track following area andtiming sync data is recorded in substantially the remainder of the trackfollowing area.

In one embodiment, each track includes a head entering end whereat ahead means rotates into recording or reproducing relation with therecord medium and a head leaving end whereat the head means rotates outof recording or reproducing relation. Track following areas are disposedin the vicinity of the head entering end and in the vicinity of the headleaving end.

As one aspect of this invention, the timing sync data is comprised ofplural timing sync data blocks, each block being of predeterminedlength. The timing sync data block includes a synchronizing datapattern, identification data and error correcting data associated withthe identification data. The timing sync data blocks precede the pilotsignal in the track following area; and in those track following areasrecorded in the vicinity of the head entering end, timing sync datablocks also follow the pilot signal, thus surrounding the pilot signalin the track following area.

In an after-recording mode, the timing sync data is reproduced from thetrack following area and detected to establish a reference from whichthe after-record area is defined. As a feature, the identification dataincluded in each timing sync data block identifies the position of thetiming sync data block within the track following area. A preset countwhich represents the position of the scanning head means along the trackis produced in response to each detected identification data, and thiscount is loaded into a counter which counts clock pulses derived fromthe signals reproduced from the record medium as the record medium isbeing scanned. When the counter reaches a predetermined count, anafter-record start indication is produced to represent the start of theafter-recording area. Preferably, an after-record end indication isproduced when the counter is incremented to a second count. The featureof presetting the counter provides additional accuracy in defining theafter-recording area even if jitter, ATF errors or errors in signalreproduction may be present. Hence, the counter is accurately preset andthe after-recording area is accurately defined even if unexpected errorsin the recording or reproducing operations otherwise interfere withproper operation of the counter. In the preferred embodiment, thecounter is not preset until the identification data from n successivetiming sync data blocks are detected continuously.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the present invention solely thereto, will best beunderstood in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of recording/reproducing apparatus in whichthe present invention finds ready application;

FIGS. 2A-2D are schematic representations of a track format includingthe signals recorded by the present invention;

FIG. 3 is a schematic representation of a track pattern recorded byrotary head recording apparatus which incorporates the present inventionand which operates in a "standard play" (SP) mode;

FIG. 4 is a schematic representation of a track pattern recorded byrotary head recording apparatus which incorporates the present inventionand which operates in a "long play" (LP) mode;

FIGS. 5A-5C are schematic representations of track patterns and signalwaveforms which are useful in understanding how automatic trackfollowing is attained;

FIG. 6 is a schematic representation of another example of a trackpattern showing the pilot and timing sync data signals recorded in trackfollowing areas;

FIG. 7 is a schematic representation of yet another track patternshowing the pilot signal and timing sync data signals recorded in trackfollowing areas;

FIG. 8 is a block diagram of a preferred embodiment of apparatus inaccordance with the present invention which defines an after-recordingarea with high accuracy; and

FIGS. 9A-9F are timing diagrams which are useful in understanding theoperation of the apparatus shown in FIG. 8.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

One example of rotary head recording/reproducing apparatus in which thepresent invention finds ready application is illustrated in the blockdiagram shown in FIG. 1. It is assumed that this apparatus is adapted torecord and reproduce video, audio and subcode signals in digital form ona magnetic tape. Nevertheless, it will be apparent that the presentinvention can be used in apparatus which records only digital videosignals or digital audio signals or other types of information signalsin parallel tracks on a record medium not necessarily limited tomagnetic tape. In the embodiment wherein digital video signals arerecorded, it will be appreciated that one frame of digital videoinformation, along with associated digital audio information and subcodedata are recorded in a plurality of tracks. For example, and as has beenproposed, one frame of digital video information in the NTSC format maybe recorded in ten tracks. Separate head assemblies HA and HB havingdifferent azimuth angles and angularly spaced apart by, for example,180°, are used to record and reproduce successive tracks on the recordmedium. By using different azimuth angles, the phenomenon known asazimuth loss is turned to account to minimize undesired cross-talkinterference that may be picked by, for example, head HA from anadjacent track previously recorded by head HB. Although each assembly isillustrated in FIG. 1 as comprising a single head, it will beappreciated that each head assembly may be formed of two or more closelyspaced heads, admitting of different azimuth angles and adapted torecord/reproduce a like number of parallel tracks substantiallysimultaneously.

The apparatus shown in FIG. 1 includes a recording section comprised ofa processing circuit 1, a multiplexer 5, a pilot and timing sync datagenerator 6, a control signal generator 7 and a channel encoder 9.Processing circuit 1 includes input terminals 2, 3 and 4 to whichdigital video, digital audio and subcode signals, respectively, aresupplied. Processing circuit 1 may be of a conventional type adapted tocompress the digital video signals, for example, by orthogonal transformencoding, such as discrete cosine transformation (DCT) and variablelength coding. In addition, the compressed digital video signal may befurther encoded by using conventional error correction codes. Theprocessing circuit also may include suitable audio processing circuitryto compress and error-correct the digital audio signal supplied theretovia input terminal 3. The precise construction and operation ofprocessing circuit 1 forms no part of the present invention per se; andin the interest of brevity and to avoid unnecessary detail andcomplexity, further description of this processing circuitry is omitted.

Pilot and timing sync data generator 6 is adapted to generate a pilotsignal and also timing sync data, both limited to a predetermined timeduration corresponding to a track following area. The pilot signaladmits of a predetermined frequency; and as will be described, dependingupon the particular track following area in which the pilot signal isrecorded, this frequency may be a single frequency f₁ or may befrequency f₁ followed by a different frequency f₂. The pilot frequenciesf₁ and f₂ may be produced by frequency-dividing a system clock signalwhose repetition rate is substantially higher than f₁ or f₂.

Generator 6 also generates timing sync data which, as will be describedbelow, is comprised of a plurality of timing sync data blocks, eachblock being of predetermined length and each block including asynchronizing data pattern (such as, for example, an alternating bitpattern), identification data (referred to hereinafter as ID data) anderror correcting data associated with such ID data. As will also bedescribed, the timing sync data blocks precede the pilot signal; and inthose track following areas which precede the information signal area ofa track, timing sync data blocks also are recorded in the trackfollowing area in both preceding and following relationship with respectto the pilot signal. This is shown more particularly in FIGS. 2B and 2C,discussed below. It will be appreciated, therefore, that pilot andtiming sync data generator 6 operates to generate a pilot signal duringa portion of each track following area (the pilot signal may be offrequency f₁ or of frequency f₁ followed by frequency f₂), and in theremainder of the track following area, generator 6 generates a pluralityof timing sync data blocks. One of ordinary skill in the art willreadily appreciate how the pilot signal and timing sync data blocks maybe generated, and further description of the construction of generator 6is not necessary.

Multiplexer 5 is coupled to processing circuit 1 and to pilot and timingsync data generator 6 and is responsive to a control signal suppliedthereto from control signal generator 7 to time division multiplex thedigital information signals supplied from the processing circuit and thepilot and timing sync data supplied from generator 6. The control signalgenerator is coupled to a system controller 8 which establishes, interalia, recording, reproducing and after-recording modes. The systemcontroller also controls the control signal generator to supply asuitable multiplex control signal to multiplexer 5, whereby either thepilot and timing sync data supplied by generator 6 or the digitalinformation supplied by processing circuit 1 are coupled to the outputof the multiplexer. More particularly, control signal generator 7produces a track following control signal of a duration substantiallyequal to a track following period and an information control signal of aduration substantially equal to an information period. Thus, during thetrack following period, multiplexer 5 couples to channel encoder 9 thepilot and timing sync data; and during the information period, themultiplexer couples to the channel encoder the digital audio, video andsubcode information. Thus, control signal generator 7 operates inconjunction with multiplexer 5 to define the allocated track followingand information areas in each track.

Channel encoder 9 is adapted to encode the signals supplied thereto frommultiplexer 5 in conventional recording codes, such as one or more of1,8 code, MFM code, MTFM, or the like. The encoded signals produced bythe channel encoder are coupled to rotary head assemblies HA and HB viarecord amplifiers 10A and 10B and the record contacts r ofrecord/playback switches 11A and 11B, respectively. Thus, when headassembly HA is rotated into a recording relation with the record medium,the encoded signals produced by channel encoder 9 are supplied to headassembly HA via record amplifier 10A. Similarly, when head assembly HBrotates into recording relation with the record medium, the encodedsignals produced by channel encoder 9 are supplied to head assembly HBby recording amplifier 10B. For the embodiment wherein the encodedsignals are recorded on a magnetic tape, successive, parallel obliquetracks are recorded by rotary head assemblies HA and HB.

Before describing the track format which is recorded by the recordingsection of the illustrated apparatus, reference is made to thereproducing section shown in FIG. 1 which includes a channel decoder 13,a timebase corrector 14, a processing circuit 16 and a timing syncdetector 17. Channel decoder 13 operates in a manner complementary tothat of channel encoder 9 and is coupled to rotary head assemblies HAand HB by playback amplifiers 12A and 12B and the playback contacts p ofrecord/playback switches 11A and 11B, respectively. The channel decoderthus recovers from the reproduced signals the pilot and timing sync datathat had been generated by generator 6 and also the video, audio andsubcode information that had been produced by processing circuit 1.

The output of channel decoder 13 is coupled to timebase corrector 14 andalso to an automatic track following (ATF) circuit 15. The ATF circuitoperates to detect a tracking error by sensing the reproduced pilotsignal and, depending upon the detected tracking error, the speed atwhich the record medium is transported is controlled so as to minimizesuch error. For example, if the record medium is a magnetic tape drivenby a capstan, the tracking error detected by ATF circuit 15 is used in aservo loop to control the capstan motor, thereby eliminating suchtracking error.

Timebase corrector 14 may be of conventional construction and is adaptedto remove timebase errors, such as jitter or other timebase deviations,from the reproduced signals. Since timebase correctors are devices whichare known to those of ordinary skill in the art, further descriptionthereof is not provided herein.

Timebase corrector 14 is coupled to processing circuit 16 which operatesin a complementary manner-to processing circuit 1 and serves to recoverfrom the reproduced, timebase corrected signals video, audio and subcodesignals at output terminals 18, 19 and 20, respectively. Processingcircuit 16 may include error correcting circuitry to detect and correcterrors in the various digital signals supplied thereto, such as thedigital audio signal that is reproduced from the record medium. It willbe appreciated that errors in the digital video signal likewise may becorrected or compensated. Processing circuit 16 forms no part of thepresent invention per se and is not described further. It will berecognized, however, that the processing circuit recovers digital video,audio and subcode signals at output terminals 18, 19 and 20,respectively.

Timing sync detector 17 is coupled to timebase corrector 14 and isadapted to detect the timing sync data included in the track followingareas scanned by heads HA and HB. A preferred embodiment of the timingsync detector is described in greater detail below in conjunction withFIG. 8. Suffice it to say that the timing sync detector operates todetect the ID data included in each timing sync data block and uses thatID data to establish the after-record area in which information data isafter-recorded. Timing sync detector 17 is coupled to control signalgenerator 7, the latter being responsive to after-record area definingsignals produced by the timing sync detector to control processingcircuit 1 and multiplexer 5 so as to after-record audio, video orsubcode information in the defined after-record area. Thus, when theestablished after-record area is scanned by heads HA and/or HB,processing circuit 1 and multiplexer 5 are suitably controlled to recordthe appropriate information signals in the established after-recordarea. As a result, there is no erroneous or inadvertent erasure orover-writing of pre-recorded signals. Rather, only those signals whichare to be replaced are over-written.

Processing circuit 1 and multiplexer 5 are controlled by the controlsignal produced by control signal generator 7 to record successiveoblique tracks on the record medium in the track format shownschematically in FIG. 2A. For convenience, the left side of the trackshown in FIG. 2A is referred to as the head entering end (or "in side")and that portion of the track shown at the right side of FIG. 2A isidentified as the head leaving end (or "out side"). Those sections ofthe track which are shown as cross-hatched lines are identified asmargins and interblock gaps in which data is not recorded. The length ofeach section is represented in terms of bytes; and it is seen thatdata-free margins are recorded at the head entering and head leavingends of the track of a length approximately equal to 450 bytes.

Information signal areas are identified as an audio information area(shown as AUDIO 1) which precedes a video area (VIDEO), the video areabeing followed by another audio area (shown as AUDIO 2) and this audioarea is followed by the subcode area (SUBCODE). Each information area ispreceded by a preamble and followed by a postamble which containrepetitive 1,0 patterns having a frequency equal to or a multiple of thedata clock frequency of the digital audio, video and subcodeinformation. The clock frequency recorded in these "amble" areas thusmay be recovered by a phase locked loop (PLL) which extracts such clockpulses in order to synchronize the clock in the reproducing sectionnormally used to recover information from the track.

A track following area ATF1 is disposed in the vicinity of the headentering end of the track shown in FIG. 2A and another track followingarea ATF2 is disposed in the vicinity of the head leaving end. A timingpreamble section, identified as "T-amble" precedes the track followingarea ATF1 and a clock signal may be recorded in this T-amble area tosynchronize the clock normally used to detect the recorded timing syncdata.

Information recorded in audio information area AUDIO 1 or videoinformation area VIDEO or audio information area AUDIO 2 or subcodeinformation area SUBCODE are adapted to be after-recorded. Thus, afterthe information shown in the track of FIG. 2A has been recorded, one ormore of the information areas AUDIO 1, VIDEO, AUDIO 2 and SUBCODE may beafter-recorded at a later time. The present invention defines theafter-recording areas for AUDIO 1, VIDEO, AUDIO 2 and SUBCODE, as willbe described.

Although separate audio information areas AUDIO 1 and AUDIO 2 areillustrated in FIG. 2A, it will be appreciated that a single audioinformation area can be provided, such as by extending the length ofarea AUDIO 1 and deleting area AUDIO 2.

As will be described, by defining an information signal area, such asthe audio information area AUDIO 1, with high accuracy, audioinformation may be after-recorded in area AUDIO 1 without undesirablyextending the after-recording area into the VIDEO area and, thus,avoiding the undesired erasure or over-writing of information in theVIDEO area.

The format of track following areas ATF1 and ATF2 when informationsignals are recorded in standard play (SP) and long play (LP) modes areillustrated in FIGS. 2B and 2C. From FIG. 2A, it is seen that the lengthof each track following area ATF1 and ATF2 is equal to 180 bytes. It isappreciated that head assemblies HA and HB scan successive tracks A andB. respectively, across the record medium. Assuming that each track Aand B admits of the same format shown in FIG. 2A, the signal content oftrack following area ATFI in track A differs from the signal content oftrack following area ATF1 in track B. In accordance with one embodimentof the present invention, in the SP mode, a pilot signal of frequency f₁is recorded in a portion of track following area ATF1, as shown in FIG.2B, and timing sync data blocks are recorded in the remainder of thistrack following area. In the illustrated embodiment, six timing syncdata blocks [1], [2], . . . [6] precede pilot signal f₁, and fourteentiming sync data blocks [17], [18], . . . [29] and [30] follow the pilotsignal. Each timing sync data block is of predetermined data length,such as 6 bytes, and a preferred format of a timing sync data block isdescribed below in conjunction with FIG. 2D.

FIG. 2B also illustrates the signal content of track following area ATF1 recorded in track B during the SP mode. Here, the pilot signal iscomprised of two successive pilot frequencies f₁ and f₂, these twofrequencies being preceded by eleven timing sync data blocks [1], [2], .. . [10] and [11]. Here too, the timing sync data is of predeterminedlength, such as 6 bytes, and exhibits the same format as the timing syncdata blocks recorded in track A. It is appreciated that the trackfollowing areas recorded in tracks A and tracks B contain the pilotsignal recorded in a portion of the track following area and theremainder of the track following area contains a plurality of timingsync data blocks. The pilot signal admits of a single frequency signalf₁ in, for example, track A, and the pilot signal consists of frequencyf₁ recorded in one portion of the track following area followed byfrequency f₂ recorded in a succeeding portion of the track followingarea in track B.

In the SP mode, the track pitch of the record track shown in FIG. 2A is9 μm, the offset distance D_(x) between the beginning of track A and thebeginning of track B (best seen in FIG. 3) is 4.54 μm, the length of thetrack following area ATF is 22.67 μm (this length is equal to 180 bytes)and the width of the head which is used to record the track is 10.5 μm.On the other hand, when data is recorded in the LP mode, the speed atwhich the record medium is transported is slower than the transportspeed used in the SP mode. Consequently, the track pitch in the LP modeis 6 μm, the offset distance D_(x) between the beginning of track A andthe beginning of track B is 3.51 μm and the length of the trackfollowing area ATF is 33.48 μm. Of course, since the same head assemblyis used for recording in both the SP and LP modes, the head widthremains at 10.5 μm. As shown in FIG. 2C, the track following area ATF1recorded in track A in the LP mode contains the pilot signal offrequency f₁ recorded in a portion of the track following area, thispilot signal being preceded by eleven timing sync data blocks [1], [2],. . . . [10] and [11]; and an additional nine timing sync data blocks[22], [23], . . . [29] and [30] are recorded in the remainder of thetrack following area following pilot signal f₁. As also shown in FIG.2C, pilot signals of frequency f₁ followed by frequency f₂ are recordedin a portion of track following area ATF1 in track B, these pilotsignals being preceded by fourteen timing sync data blocks [1], [2], . .. [13] and [14]. Although the formats of the track following areas intracks A and B are quite similar in the SP and LP modes, a comparison ofFIGS. 2B and 2C indicates that specific details in these formats differfrom one mode to the next.

FIG. 2D is a schematic illustration of the data format of each 6-bytetiming sync data block. As shown, each timing sync data block includes asynchronizing data pattern of a length equal to 2 bytes, followed byidentification (ID) data, also formed of 2 bytes, followed by errorcorrecting data (IDP) associated with the ID data, this error correctingdata being formed of 1 byte and, for example, may consist of paritydata. This parity data may be formed of four bits. Finally, the timingsync data block includes one byte of blank data.

The two bytes of ID data may be formed of the following bits:

In the first byte, the most significant bit identifies the recordingmode as either SP or LP.

The seventh bit is not defined.

The sixth and fifth bits are used to identify the type of data which maybe after-recorded, such as whether the data is audio data, video data orsubcode data.

The fourth bit to the least significant bit are not defined.

In the second byte, the most significant bit, the seventh bit and thesixth bit are not defined.

The fifth bit to the least significant bit constitute a 5-bit numberwhich identifies the timing sync data block. In the examples shown inFIGS. 2B-2C, this 5-bit number identifies the position of the timingsync data block in the track following area, such as block number [1] orblock number [2], . . . or block number [30]. It will be appreciated,then, that the timing sync data block number represented by the ID datathus represents the distance from that timing sync data block to thebeginning of the audio area or the beginning of the video area or thebeginning of the subcode area, depending upon which type of informationis to be after-recorded. For example, since the length of trackfollowing area ATF1 is known (e.g. it is 180 bytes) and the length ofthe audio preamble and intergap also is known (e.g. it is 174 bytes),then the distance from any timing sync data block to the beginning ofthe AUDIO 1 area likewise is known once the position of that timing syncdata block within the track following area is sensed. Similarly, thedistance from any detected timing sync data block to the beginning ofthe VIDEO area or to the beginning of the AUDIO 2 area or to thebeginning of the SUBCODE area is known once the identification, orlocation within the track following area of that timing sync data blockis detected. It also is recognized that the position of the timing syncdata block represents the position of head HA or HB as the head scansthe record track.

The track patterns in the vicinity of the head entering end and the headleaving end of successive record tracks A and B for the SP mode areillustrated in FIG. 3. It is assumed that rotary head assemblies HA andHB scan tracks A and B in the direction represented by x from the headentering end to the head leaving end. The offset distance D_(x) betweenthe beginning of track A and the beginning of track B is equal to theoffset distance between the end of track A and the end of track B. Thepilot signal in the track following areas at the head entering end andat the head leaving end of tracks A and B are shown as pilot signal f₁and pilot signal f₂, as the case may be, and the timing sync data blocksare represented as f_(T). In one embodiment, the pilot signal f₁ or f₂is recorded in a track following area over a distance equal to 2D_(x).It is seen that in track following area ATF1 in track A, the pilotsignal f₁ is recorded over the length 2D_(x) and is preceded andfollowed by timing sync data blocks f_(T). In track following area ATF1of track B, timing sync data blocks f_(T) first are recorded and thenthe pilot signal f₁ is recorded for the length 2D_(x) followed by thepilot signal f₂ which is recorded for another length 2D_(x).

This track pattern recorded in track following areas ATF1 at the headentering end are reversed in track following areas ATF2 at the headleaving end. Thus, the pattern formed of the pilot signal and timingsync data blocks recorded in track following ATF2 for track B is seen tobe the same as the pattern recorded in track following area ATF1 fortrack A. Similarly, the pattern of the timing sync data blocks f_(T) andpilot signals f₁ and f₂ recorded in track following area ATF2 of track Ais similar to the pattern recorded in track following area ATF1 of trackB. It will be appreciated that pilot and timing sync data generator 6 ofFIG. 1 may be constructed in a relatively simple, straightforward mannerto produce the record signal having the format shown in FIGS. 2B-2D andrecorded with the pattern shown in FIG. 3. For example, a suitable burstgenerator (or generators) may be used to provide the pilot signal f₁ andthe pilot signal f₂ each for a duration corresponding to the length2D_(x). Also, a suitable ID data generator may be incremented to producethe successive timing sync data blocks having successive ID data of thetype discussed above. As an example, a counter may be incremented from acount of [1] to a count of [30] and then reset, thereby generatingsuccessive timing sync data blocks having the ID pattern shown in FIG.2B.

The pilot signal f₁ or f₂ may be generated by dividing the frequency ofthe system clock by a suitable divisor. For example, if the system clockf_(o) is on the order of about 21.65 MHz, then the pilot frequency f₁may be f_(o) /33=656 kHz; and pilot frequency f₂ may be f₂ =f_(o)/22=984 kHz. It will be appreciated that these values of the pilotfrequencies f₁ and f₂ are intended to be examples only. Other suitablepilot frequencies may be used, provided that f₁ ≠f₂. Preferably, f₁ <f₂,although this relationship simply is preferable and is not a necessity.

FIG. 4 is a schematic representation of the track following areas ATF1and ATF2 recorded in tracks A and B by head assemblies HA and HB,respectively, operating in the LP mode. It is seen that the offsetdistance D_(x) from the beginning of track A to the beginning of track Bin the LP mode is less than the offset distance D_(x) in the SP mode.When recording the pilot signal in the LP mode, the pilot signal f₁ isrecorded over a distance equal to 3D_(x) and the pilot signal f₂ isrecorded over a distance equal to 2D_(x). Although not identified byspecific legend in FIG. 4, it will be recognized that in track followingarea ATF1 for track A, the timing sync data blocks are recorded inadvance of and then following pilot signal f₁, whereas in track B, thetiming sync data blocks are recorded in advance of pilot signal f₁ whichis followed by pilot signal f₂. As was the case when recording in the SPmode, the pattern of timing sync data blocks and pilot signals recordedin track following area ATF2 in track B is substantially the same as thepattern recorded in track following area ATF1 in track A; and thepattern recorded in track following area ATF2 in track A issubstantially the same as the pattern recorded in track following ATF1in track B. It will be understood that the pilot frequencies f₁ and f₂recorded in the LP mode are the same as the pilot signal frequencies f₁and f₂ recorded in the SP mode; and as a numerical example, f₁ =656 KHzand f₂ =984 KHz.

The pilot signal frequency pattern shown in FIGS. 3 and 4 permitaccurate detection of tracking errors and facilitate the correction ofsuch tracking errors. However, tracking error detection and correctioncan be readily obtained by recording pilot signals in other patterns;and the pilot signals need not be limited solely to the patterns shownin FIGS. 3 and 4. An example of yet another pattern of pilot signalswhich facilitate tracking error detection and correction is shown inFIG. 5A, which illustrates the recording of pilot signals of frequencyf₁ in tracks A of the track following area disposed in the vicinity ofthe head entering end and of frequency f₂ in tracks B. Similarly, FIG.5C illustrates the recording of pilot signals of frequency f₂ in tracksA in the track following area at the head leaving end of each track andfrequency f₁ in tracks B. For convenience, the recording of timing syncdata blocks in tracks A and B in the track following areas at the headentering end and at the head leaving end of the respective tracks is notillustrated.

The manner in which the pilot signals recorded in the patterns shown inFIGS. 5A and 5C are used to detect and correct tracking errors now willbe described in conjunction with the waveforms shown in FIG. 5B. Forsimplicity, it is assumed that the width of the head, such as head HA orhead HB, is equal to the pitch of each track A and B and, moreover, itis assumed that there is substantially no variation in the waveform ofthe pilot signal which is reproduced from each track. It also is assumedthat the azimuth angle of head HA is equal to the azimuth angle of thehead which recorded pilot signals in tracks A; and the azimuth angle ofhead HB is equal to the azimuth angle of the head which recorded thepilot signals in tracks B. Accordingly, when head HA scans a track A toreproduce the pilot signals that had been recorded in the trackfollowing areas of the respective tracks in the vicinity of the headentering end, pilot signal of frequency f₁ is reproduced with arelatively higher amplitude and, because of azimuth loss, the pilotsignal of frequency f₂ which is reproduced as a cross-talk componentfrom one or the other of adjacent tracks B admits of a much loweramplitude. This is shown in FIG. 5B(i). A suitable detector adapted todetect the pilot signal of frequency f₁, for example, a detector that isparticularly tuned to this frequency, generates an output pulse PO shownin FIG. 5B(ii). One-shot pulse generators, such as monostablemultivibrators, respond to the trailing edge of pulse PO to producesampling pulses P1 and P2 shown in FIG. 5B(iv). The inherent time delaysof such pulse generators, or monostable multivibrators, are such thatsampling pulses P1 and P2 are timed to occur substantially in the middleof the period during which the cross-talk component of pilot signal f₂is picked up from adjacent tracks B. These sampling pulses sample thecross-talk pilot signal f₂ picked up by head HA, and FIG. 5B(iii)illustrates the envelope of these cross-talk components as E1 and E2,respectively. Accordingly, sampling pulse P1 samples the envelope of thecross-talk pilot signal f₂ which, as shown in FIG. 5B(v), results in thesampled level E1; and sampling pulse P2 samples the envelope of thecross-talk pilot signal f₂ which, as shown in FIG. 5B(vi), results inthe sampled level E2.

It is appreciated that, when head HA is properly centered on track A inFIG. 5A, the level of the cross-talk pilot signal f₂ picked up by headHA from each of adjacent tracks B is equal. However, if head HA driftsin the upward direction, the level of the cross-talk pilot signal f₂sampled by sampling pulse P1 is greater than the level of the cross-talkpilot signal f₂ sampled by pilot signal P2. The difference between thesampled cross-talk envelopes (E1-E2) represents the direction and degreeby which head HA drifts from the center line of track A. Accordingly, asubtraction circuit is provided to subtract the sampled cross-talk pilotsignal E2 from the sampled cross-talk pilot signal E1 (or vice versa) toproduce a tracking error indication. This tracking error indication isused as a drive control signal to drive the capstan motor whichtransports the magnetic tape, thereby providing tracking controlcorrection. Of course, if other record media are used, theaforementioned tracking error indication is fed back to the mediumtransport arrangement so as to drive the medium in a manner whichcorrects for this detected tracking error.

A similar tracking error detection arrangement may be used to sense thetracking error of heads HA and HB as such heads scan the head leavingend of respective tracks. In one embodiment, the tracking error obtainedwhen head HA, for example, scans a track following area in the vicinityof the head entering end is averaged with the tracking error detectedwhen that head scans the track following area in the vicinity of thehead leaving end so as to produce an average tracking error indication.Tape speed and, thus, tracking error correction, is controlled as afunction of this average tracking error indication.

It is appreciated that, by relying upon tracking error indicationsproduced from head HA as well as head HB, the possibility that a validtracking error indication from one of these heads may not be producedbecause of "clogging" means that tracking area correction may beachieved simply by relying upon the tracking error indication derivedfrom the other head. It also will be appreciated that if the trackingerror indication produced by one head appears to be of a zero level butthe tracking error indication produced by the other head is not, thepresence of, for example, head clogging may be readily detected.

FIGS. 6 and 7 are schematic representations of still further trackpatterns of pilot signals that may be recorded in the track followingarea of each track. For simplification, FIGS. 6 and 7 do not illustratethe timing sync data blocks that also are recorded. The pattern shown inFIG. 6 is recorded during the SP mode and that shown in FIG. 7 isrecorded during the LP mode. In both the SP and LP modes, the pilotsignal admits of only a single frequency, such as f₁ (or f₂). In oneexample, the pilot frequency may be on the order of about 1 MHz.

Each track following area in the SP mode may be thought of as beingdivided into five successive segments, each admitting of a length equalto D_(x), the offset distance between adjacent tracks. As shown, in eachof tracks A, the pilot signal is recorded in the first D_(x) segment andthen in the last D_(x) segment. In each of track B, the pilot signal isrecorded only in the third D_(x) segment, that is, in the middle of thetrack following area. The pattern in which the pilot signal is recordedin the LP mode, as shown in FIG. 7, is similar to that recorded in theSP mode. In the LP mode, each track following area may be thought of asbeing divided into eight successive segments, each of length D_(x). Intrack A, the pilot signal is recorded in the first two D_(x) segmentsand in the last two D_(x) segments. In track B, the pilot signal isrecorded only in the fourth and fifth D_(x) segments, which is seen tobe the middle of the track following area.

In both the SP and LP modes, tracking errors are detected as follows:When head HA scans track A, the pilot signal recorded in track A isreproduced with a relatively high amplitude, and the trailing edge ofthe pulse produced from the detected pilot signal is used to producesampling pulses which sample the cross-talk pilot signal componentspicked up by head HA from upper adjacent track B and from lower adjacenttrack B. Any difference in the sampled cross-talk pilot signalcomponents is indicative of the direction and magnitude of a trackingerror.

Similarly, when head HB scans tracks B, the pilot signal reproduced fromtrack B admits of a relatively large amplitude; and the trailing edge ofthe pulse produced from this pilot signal is used to produce samplingpulses which coincide with the cross-talk pilot signal reproduced byhead HB from upper adjacent track A and from lower adjacent track A.Here too, any difference between the sampled cross-talk pilot signals isindicative of the direction and degree of tracking error.

FIGS. 6 and 7 illustrate the pilot signal pattern recorded in the trackfollowing areas disposed in the vicinity of the head entering end ofeach track. It will be appreciated that a similar pilot signal patternis recorded in the track following areas disposed in the vicinity of thehead leaving end of each track. For example, the pattern recorded in thetrack following area in the vicinity of the head entering end of track Amay be recorded in the track following area in the vicinity of the headleaving end of track B. Consequently, tracking errors present at thehead entering end as well as at the head leaving end are detected andcorrected.

Turning now to FIG. 8, there is illustrated a block diagram of oneembodiment of the present invention which operates to establish anafter-record area in the audio, video or subcode information areareferenced from the timing sync data blocks which have been recorded inthe track following area, as shown for example in FIGS. 2A-2D. It willbe appreciated that the block diagram shown in FIG. 8 is a preferredembodiment of timing sync detector 17 and that portion of control signalgenerator 7 which is relevant to this invention. The after-record areadefining apparatus shown in FIG. 8 is comprised of a timing syncdetector 21, an ID continuity check circuit 23, preset count selectorcircuits 24A and 24B, position counters 25A and 25B and decoders 26A and26B. It will be appreciated that preset count selector circuit 24A,position counter 25A and decoder 26A are included in a channel A andnormally are responsive to timing sync data blocks reproduced from trackA by head HA; and preset count selector circuit 24B, position counter25B and decoder 26B are included in a channel B responsive to timingsync data blocks reproduced from track B by head HB. The circuitsincluded in channel A are substantially the same as those included inchannel B and, in the interest of brevity, only one of these channels isdescribed in detail.

Timing sync detector 21 is adapted to detect the timing sync data blocksshown in, for example, FIG. 2D. As an example, the particularsynchronizing pattern included in the 2-byte sync portion may besufficiently unique as to be readily detected. Upon detection, the IDdata and ID parity data included in the detected timing sync data blockare supplied to an ID error correcting circuit 22 for the purpose ofcorrecting the ID data included in the detected timing sync data block.The ID error correcting circuit may be of a known type which uses IDparity data to detect errors present in the ID data and to correct thoseerrors. Assuming that the ID data is correct or correctable, ID errorcorrecting circuit 22 is adapted to supply to ID continuity checkcircuit 23 a data valid signal b which admits of a relatively high levelif the ID data supplied to the ID error correcting circuit is correct orcorrectable, and also supplies to the ID continuity check circuit thecorrect (or corrected) ID data itself.

ID continuity check circuit 23 is adapted to detect when a predeterminednumber n (preferably, n>2) of consecutive ID data has been detected bytiming sync detector 21. For example, when the timing sync data block[1] included in a track following area is received, the ID datarepresenting this timing sync data block sets a counter included in theID continuity check circuit. Then, upon the detection of each successivetiming sync data block, this count is incremented by one. The IDcontinuity check circuit includes a comparator which compares theincremented count of this counter to the ID data included in thenext-following timing sync data block. If the incremented count matchesthe ID data, a continuity counter is incremented by one. When thiscontinuity counter reaches a predetermined count n, such as n=3, thusindicating that three successive, consecutive timing sync data blockshave been detected, a counter load signal c is produced by ID continuitycheck circuit 23. However, if a discontinuity is present in the timingsync data blocks which are detected, for example, if, because of errorsin the reproduced data, as may be caused by jitter, dropout or the like,the ID data representing timing data sync block [3] is not detected, IDcontinuity check circuit 23 does not produce counter load signal c. But,if timing sync data blocks [4], [5] and [6] are properly detected insuccession, then the ID continuity check circuit generates the counterload signal.

The counter load signal produced by ID continuity check circuit 23 iscoupled to position counters 25A and 25B, respectively, for the purposeof loading a preset count into these counters, as will be described.

The ID continuity check circuit also couples to another output thereofthe ID data which represents the presently detected timing sync datablock and which is supplied thereto from timing sync detector 21 by wayof ID error correcting circuit 22. This present ID data is coupled topreset count selector circuits 24A and 24B. Each preset count selectorcircuit is adapted to produce a preset count value in response to eachID data supplied thereto. This preset count value may be thought of asrepresenting the distance from the present timing sync data blockrepresented by the ID data supplied to the preset count selector circuitto the beginning of the after-record area. Thus, as each timing syncdata block is detected, the count value representing the distance fromthat timing sync data block to the beginning of the after-record areachanges. As one example thereof, each preset count selector circuit maybe formed as a look-up table that is addressed by the ID data recoveredfrom each detected timing sync data block to supply to the positioncounter coupled thereto the particular count corresponding to that IDdata.

Preset count selector circuits 24A and 24B are coupled in common toreceive the ID data recovered from the presently detected timing syncdata block; and each preset count selector circuit is coupled to aninput terminal to receive a switching pulse d which is used to selectone or the other of the preset count selector circuits for operation. Aswill be described, switching pulse d indicates whether head HA or HB isin scanning relationship with a track A or B, respectively, and as oneexample, the switching pulse admits of a relatively high level to enablepreset count selector circuit 24A when head HA scans a track A andadmits of a relatively low level to enable preset count selector circuit24B when head HB scans track B.

Preset count selector circuit 24A is coupled to position counter 25A andis adapted to load, or preset, the position counter with the presetcount selected in response to the present ID data supplied to the presetcount selector circuit, provided that ID continuity check circuit 23produces counter load signal c. The position counter is adapted to countdata clock pulses which are recovered from the record medium when headHA scans track A. Although not shown, a phase locked loop may beprovided to recover these data clock pulses which may be recorded in,for example, the preamble, postamble or T-amble areas of a record track,such as shown in FIG. 2A. These data clock pulses also may be recoveredfrom the synchronizing bit pattern included in each timing sync datablock. In any event, the clock pulses which are counted by positioncounter 25A are produced as head HA scans a record track; and it will beappreciated that the instantaneous count of the position counter thusrepresents the instantaneous position of the head along the trackscanned thereby.

Decoder 26A is coupled to position counter 25A and is adapted to decodeparticular counts to which the position counter is incremented. Forexample, when the position counter attains a maximum count, this maximumcount is decoded to produce a reset signal RST which is fed back bydecoder 26A to a reset terminal of position counter 25A. As will bedescribed, this maximum count N_(max) is reached when the head rotatesto the head leaving end of the record track shown in FIG. 2A.

Decoder 26A also is adapted to sense when the count of position counter25A reaches a predetermined first count N₁ and a second count N₂. Thisfirst count N₁ corresponds to the position of the head at the beginningof an after-record area; and the count N₂ corresponds to the position ofthat head when it reaches the end of the after-record area. For example,counts N₁ and N₂ may define the AUDIO 1 area, the VIDEO area, the AUDIO2 area or the SUBCODE area shown in FIG. 2A. In one embodiment, decoder26A produces an after-record signal f which admits of a relatively highlevel when the head scans the after-record area.

The interconnection and operation of preset count selector circuit 24B,position counter 25B and decoder 26B are substantially the same as thatdiscussed above in conjunction with these same circuits included inchannel A. Although both position counters and decoders operate whenboth heads HA and HB scan tracks A and B, respectively, it isappreciated that only one or the other position counter is preset by thecount produced by preset count selector circuit 24A or 24B, dependingupon whether head HA or head HB then is scanning the record track.

The manner in which the apparatus illustrated in FIG. 8 operates nowwill be described in conjunction with the timing and waveform diagramsshown in FIGS. 9A-9F. FIG. 9A schematically represents the timing syncdata blocks recorded in track following areas ATF1 and ATF2 at the headentering and head leaving ends of each track. For simplicity, only fivetiming sync data blocks are illustrated; and it is appreciated that FIG.9A does not illustrate the presence of pilot signals f₁ and f₂ which arepresent in the track following areas. In any event, FIG. 9Aschematically represents the detected timing sync data blocks suppliedto ID error correcting circuit 22 by timing sync detector 21.

FIG. 9B schematically illustrates the valid ID data pulse produced by IDerror correcting circuit 22 when valid, or correct, identification datais detected. This valid ID data pulse enables ID continuity checkcircuit 23 to sense the continuity of successive ID data which isrecovered from the track following area. If, as discussed above, nsuccessive timing sync data blocks are detected, the ID continuity checkcircuit produces a counter load signal c; and the production of thissignal is schematically illustrated in FIG. 9C. If, for example, n=3,the counter load signal is generated in response to each third timingsync data block, assuming that there is no discontinuity or errors indetecting those blocks.

FIG. 9D illustrates head switching pulse d and, as discussed above, itis assumed that head HA scans track A when head switching pulse d admitsof a relatively high level; and head HB scans track B when the headswitching pulse admits of a relatively low level. When the headswitching pulse exhibits its high level, preset count selector circuit24A is enabled and responds to the ID data included in the presentlydetected timing sync data block supplied thereto by ID continuity checkcircuit 23 to produce a count value corresponding to this ID data. Asmentioned above, this count value may be thought of as representing thedistance from the present timing sync data block to the beginning of theafter-record area. This preset count also may be thought of asrepresenting the distance from the beginning of the record track to thedetected timing sync data block. In any event, this count represents thepresent position of the head as it scans the record track and is coupledto position counter 25A. If ID continuity check circuit 23 has producedthe counter load signal c, position counter 25A is loaded, or presetwith this count. The position counter counts the aforementioned dataclock pulses so as to increment its count, as schematically depicted inFIG. 9E, from a reset count to a maximum count. It is expected that ifthere is no jitter or error in recovering data clock pulses, the presetcount to which position counter 25A is loaded will be the count normallyreached by the position counter at that time. However, andadvantageously, by presetting the position counter to a countcorresponding to the ID data in the presently detected timing sync datablock, the position counter is preset to its proper count even ifjitter, dropout or other errors may be present to interfere with theaccurate recovery of data clock pulses.

As the count e of position counter 25A increments, such as such in FIG.9E, decoder 26A senses when this count is equal to the count of N₁. Atthat time, the decoder produces an output pulse f, such as shown in FIG.9F, whose leading edge corresponds to the count of N₁ and whose trailingedge corresponds to the count of N₂. The duration of this pulse fproduced by decoder 26A defines the after-record area and is referred toas the after-record pulse. That is, the leading edge of this pulseprovides the after-record start indication and the trailing edgeprovides the after-record end indication. As mentioned above, theduration and position of this pulse f is determined by the predeterminedcounts N₁ and N₂ and establishes the after-record area in substantialcoincidence with the AUDIO 1 area, the VIDEO area, the AUDIO 2 area orthe SUBCODE area, as may be desired.

It is seen that, even after the after-record pulse f is produced,position counter 25A continues to increment its count until it reachesthe maximum count N_(max). This maximum count is decoded by decoder 26Ato return a reset pulse RST to the position counter, thereby resettingthe count thereof. A comparison of FIGS. 9A and 9E indicates theposition counter is reset at the time that a head reaches the headleaving end of a track, which substantially coincides with the time thatthe next head rotates to the head entering end of the next track.

It is appreciated that the after-record pulse shown in FIG. 9F isproduced first by decoder 26A of channel A, then by decoder 26B ofchannel B, then by decoder 26A of channel A, and so on. Thisafter-record pulse is generated accurately, even if errors or dropoutsare present in the recovered data clock pulses or in the detected timingsync data blocks because position counters 25A and 25B are preset by thepreset counts produced by preset count selector circuits 24A and 24Bfrom the ID data actually detected in the respective timing sync datablocks. By using ID continuity check circuit 23, a reasonable assuranceis provided that the ID data is valid and correct. Nevertheless, it willbe appreciated that the ID continuity check circuit or, alternatively,the ID error correcting circuit 22 may be omitted, if desired.

In the present invention, timing sync data blocks are recorded in thetrack following area disposed in the vicinity of the head entering endas well as the track following area disposed in the vicinity of the headleaving end of each track. The ID data included in the timing sync datablocks of, for example, track following area ATF2 may be used by presetcount selector circuits 24A and 24B to produce preset counts whichrepresent the instantaneous position of head HA or head HB as the headscans the track following area ATF2, thus assuring that positioncounters 25A and 25B are preset, or loaded, with proper counts. Thismeans that if dropout or errors are present in track following area ATF1so that the timing sync data blocks therein cannot be detectedaccurately, the position counters nevertheless are preset with accuratecounts in response to the ID data detected from track following areaATF2. Consequently, the position counters will reach their predeterminedcounts N₁ and N₂ when heads HA and HB are in accurate registration withthe desired after-record area, and after-record pulse f will be producedby decoders 26A and 26B even if such dropouts or errors are present intrack following area ATF1.

It is preferred to record pilot signals f₁ and f₂ (or, in thealternative arrangements discussed above, only pilot signal f₁ need berecorded) rather than rely upon the synchronizing bit pattern of eachtiming sync data block to represent the pilot signal. This is becausethe synchronizing bit pattern of the timing sync data block typically isdetected by supplying that bit pattern through a notch filter whichblocks the frequency component of the pilot signal. This assures properdetection of the pilot frequency for tracking error detection andcorrection and also assures proper detection of each timing sync datablock. Hence, if the synchronizing bit pattern also represents the pilotsignal, this filtering operation prevents tracking error detection andcorrection from being performed accurately. Moreover, the timing syncdata block normally is code converted, such as by 6-8 conversion, whichfurther inhibits accurate detection of the pilot signal frequency if thesynchronizing bit pattern is used as the pilot signal.

Preferably, and as mentioned above, the synchronizing bit patternincluded in the sync byte of each timing sync data block may be equal toor derived from the system clock frequency.

While the present invention has been particularly shown and describedwith reference to a preferred embodiment, it will be readily appreciatedby those of ordinary skill in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention. For example, only a single track following area may berecorded, such as the track following area disposed in the vicinity ofthe head entering end of a record track. Also, the pilot signal which isused for tracking error detection and correction can be recorded inother areas of the record track and need not be limited solely to thetrack following area. For example, the pilot signal can be superimposedover the entire length of the record track.

As another alternative to the embodiment described herein, positioncounters 25A and 25B can be preset with counts derived from the ID dataincluded in timing sync data blocks disposed in track following areaATF1 only. That is, the presetting of the position counters in responseto preset counts derived from the ID data recovered from timing syncdata blocks included in track following area ATF2 can be omitted. Stillfurther, position counters 25A and 25B may be used to count referencecount pulses that are produced independently of the recovered data clockpulses. However, it is preferred to synchronize the clock pulses countedby the position counters ID with the recovered data clock pulses so thatthe position count represents the actual position of head HA or HB asthe head scans a record track. Other equivalent means may be used suchthat the instantaneous count of the position counter is an accuraterepresentation of the actual position of the head.

It is, therefore, intended that the appended claims be interpreted asincluding the embodiment described specifically herein, thosealternatives which have been discussed above and all equivalentsthereto.

What is claimed is:
 1. In rotary head recording apparatus of the typehaving first and second head means for recording respective obliquetracks on a record medium, each track including an information signalarea in which information data is recorded preceded by a track followingarea, said apparatus comprising: pilot signal generating means forgenerating a tracking control pilot signal; timing data generating meansfor generating timing sync data, said timing sync data includingidentification data which identifies the position of the timing syncdata in the track following area of the track and which is indicative ofa distance between the timing sync data and the information signal area;and control means coupled to said pilot signal and timing datagenerating means for recording said timing sync data in said trackfollowing area.
 2. The apparatus of claim 1, wherein said timing syncdata further includes a synchronizing data pattern and error correctingdata associated with said identification data.
 3. The apparatus of claim1 wherein said timing sync data is comprised of plural timing sync datablocks, each of predetermined data length.
 4. The apparatus of claim 3wherein each timing sync data block includes a synchronizing datapattern, identification data and error correcting data associated withsaid identification data.
 5. The apparatus of claim 4 wherein saidtiming sync data blocks precede said pilot signal in said trackfollowing area.
 6. The apparatus of claim 5 wherein said pilot signalexhibits a single frequency.
 7. The apparatus of claim 6 whereinadditional timing sync data blocks follow said pilot signal in saidtrack following area.
 8. The apparatus of claim 5 wherein said pilotsignal is formed as a first signal exhibiting a first frequency followedby a second signal exhibiting a second frequency.
 9. The apparatus ofclaim 1 wherein a respective track includes a head entering end whereata respective head means rotates into recording relation with the recordmedium and a head leaving end whereat said respective head means rotatesout of recording relation with said record medium, and said trackfollowing area is disposed in the vicinity of said head entering end.10. The apparatus of claim 9 further comprising an additional trackfollowing area disposed in the vicinity of said head leaving end.